Degenerative Myelopathy Testing

A New Test for DM

The collaborative efforts of Dr Joan Coates and Dr Gary Johnson and associates at the University of Missouri and Dr Kirsten Lindblad-Toh and Dr Claire Wade and associates at the Broad Institute at MIT/Harvard have resulted in identification of a mutation that is a major risk factor for the development of Degenerative Myelopathy in many breeds of dogs.

The DNA test for DM is now available through the Orthopedic Foundation for Animals (OFA). This test clearly identifies dogs that are clear (have 2 normal copies of the gene), those who are carriers (have one normal copy of the gene and one mutated copy of the gene), and those who are at much higher risk for developing DM (have 2 mutated copies of the gene). However, having two mutated copies of the gene does not necessarily result in disease. Dogs that have clinical signs or a presumptive diagnosis of DM have tested as genetically affected. A relatively high percentage of dogs in several breeds (including Boxers, Chesapeake Bay Retrievers. Pembroke Welsh Corgis, and Rhodesian Ridgebacks) have the predisposing mutation. It is important to note that there are a large number of dogs that have tested as genetically affected, but are reported as clinically normal by their owners. Information in the RESEARCH section of this website outlines continued and ongoing research that seeks to understand what triggers development of clinical symptoms in some, but not all dogs at risk. Selected dogs that can help this research are eligible for a FREE DNA test - click here to see if your dog may qualify.

FREE test results are available for samples that were submitted for DM research to the University of Missouri or the Broad Institute prior to July 15, 2008. If your dog's sample was submitted to assist the research that lead to this discovery, click here to request the test result for your dog.

Understanding the DNA Test for Degenerative Myelopathy

We have discovered a gene which is a major risk factor for degenerative myelopathy (DM). In that gene, the DNA occurs in two possible forms (or alleles). The “G” allele is the predominant form in dog breeds in which DM seldom or never occurs; you can think of it as the “Good” allele. The “A” allele is more frequent in dog breeds for which DM is a common problem; you can think of it as the “Affected” allele.

Summary: “A” allele is associated with DM; “G” allele is not associated with DM.

Since an individual dog inherits two alleles (one from the sire and one from the dam) there are three possible test results: two “A” alleles; one “A” and one “G” allele; and, two “G” alleles. Summary: Test results can be A/A, A/G, or G/G.

In the seven breeds we studied so far (Boxer, Chesapeake Bay Retriever, German Shepherd Dog, Pembroke Welsh Corgi, Cardigan Welsh Corgi, Rhodesian Ridgeback, and Standard Poodle), dogs with test results of A/G and G/G have never been confirmed to have DM. Essentially all dogs with DM have the A/A test result. Nonetheless, many of the dogs with an A/A test result have not shown clinical symptoms of DM. Dogs with DM can begin showing signs of disease at 8 years of age, but some do not show symptoms until they are as old as 15 years of age. Thus, some of the dogs who have tested A/A and are now normal may still develop signs of DM as they age. We have, however, found a few 15-year-old dogs that tested A/A and are not showing the clinical symptoms of DM. Unfortunately, at this point we do not have a good estimate of what percent of the dogs with the A/A test result will develop DM within their lifespan.

Summary: Dogs that test A/G or G/G are very unlikely to develop DM. Dogs that test A/A are much more likely to develop DM. Our research will now focus on how many A/A dogs can survive to old age without developing DM and why.

The “A” allele is very common in some breeds. In these breeds, an overly aggressive breeding program to eliminate the dogs testing A/A or A/G might be devastating to the breed as a whole because it would eliminate a large fraction of the high quality dogs that would otherwise contribute desirable qualities to the breed. Nonetheless, DM should be taken seriously. It is a fatal disease with devastating consequences for the dogs and a very unpleasant experience for the owners who care for them. Thus, a realistic approach when considering which dogs to select for breeding would be to consider dogs with the A/A or A/G test result to have a fault, just as a poor top-line or imperfect gait would be considered faults. Dogs that test A/A should be considered to have a worse fault than those that test A/G. Dog breeders could then continue to do what conscientious breeders have always done: make their selections for breeding stock in light of all of the dogs’ good points and all of the dogs’ faults. Using this approach over many generations should substantially reduce the prevalence of DM while continuing to maintain or improve those qualities that have contributed to the various dog breeds.

Summary: We recommend that dog breeders take into consideration the DM test results as they plan their breeding programs; however, they should not over-emphasize this test result. Instead, the test result is one factor among many in a balanced breeding program.